1. Field of the Invention
This invention relates to a process for the preparation of .beta.-hydroxyketones by the catalytic hydrogenolysis of 3,5-substituted-isoxazolines using a transition metal catalyst in a fixed bed reactor.
2. Description of the Prior Art
It is known in the prior art that alkyl substituted .DELTA..sup.2 isoxazolines can be catalytically reduced to .beta.-hydroxyketones using Raney nickel catalysts. The general reaction can be expressed as follows: ##STR2##
The classical method for preparing .beta.-hydroxyketones involved mixing isoxazoline, acids or buffers, and catalyst to form a slurry, adding the slurry to a reactor (known as a slurry reactor), and constantly agitating the slurry under increased temperature and pressure with addition of hydrogen gas to obtain .beta.-hydroxyketone in from 60 to 90 percent yield. There are, however, several inherent disadvantages to this process.
As indicated in the above reaction, ammonia is a major by-product of this process. Since the prior art process was performed in single batch, slurry reactor, it required the addition of an excess amount of acid or buffer in order to react with the ammonia by-product and thereby avoid deactivation of the catalyst and/or the loss of the selectivity to .beta.-hydroxy ketones.
The addition of acid to a pressurized reactor requires either (1) the use of expensive, non-corrosive acids such as boric acid, or (2) the use of glass-lined reactors suitable for use with corrosive acids such as hydrochloric acid. The excess unreacted acid in this process as well as the slurried catalyst must be removed, thereby increasing the downstream recovery costs.
A further disadvantage of this process is the substantial capital equipment cost attributed to the large reactor size which is required to afford economic feasibility on an industrial scale and which is also necessary to accommodate the agitation equipment required in slurry reactors.